add compost left_channel, right_channel

sprout/compost/formats.hpp

@@ -3,5 +3,7 @@
 
 #include <sprout/config.hpp>
 #include <sprout/compost/formats/as_pcm_wave.hpp>
+#include <sprout/compost/formats/left_channel.hpp>
+#include <sprout/compost/formats/right_channel.hpp>
 
 #endif	// #ifndef SPROUT_COMPOST_FORMATS_HPP

sprout/compost/formats/left_channel.hpp

@@ -0,0 +1,44 @@
+#ifndef SPROUT_COMPOST_FORMATS_LEFT_CHANNEL_HPP
+#define SPROUT_COMPOST_FORMATS_LEFT_CHANNEL_HPP
+
+#include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
+#include <sprout/range/adaptor/steps.hpp>
+
+namespace sprout {
+	namespace compost {
+		namespace formats {
+			//
+			// left_channel_forwarder
+			//
+			class left_channel_forwarder {};
+
+			//
+			// left_channel
+			//
+			namespace {
+				SPROUT_STATIC_CONSTEXPR sprout::compost::formats::left_channel_forwarder left_channel{};
+			}	// anonymous-namespace
+
+			//
+			// operator|
+			//
+			template<typename Range, typename T>
+			inline SPROUT_CONSTEXPR auto
+			operator|(Range&& lhs, left_channel_forwarder const& rhs)
+			-> decltype(
+				sprout::forward<Range>(lhs)
+					| sprout::adaptors::steps(2)
+				)
+			{
+				return sprout::forward<Range>(lhs)
+					| sprout::adaptors::steps(2)
+					;
+			}
+		}	// namespace formats
+
+		using sprout::compost::formats::left_channel;
+	}	// namespace compost
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_COMPOST_FORMATS_LEFT_CHANNEL_HPP

sprout/compost/formats/right_channel.hpp

@@ -0,0 +1,44 @@
+#ifndef SPROUT_COMPOST_FORMATS_RIGHT_CHANNEL_HPP
+#define SPROUT_COMPOST_FORMATS_RIGHT_CHANNEL_HPP
+
+#include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
+#include <sprout/range/adaptor/steps.hpp>
+
+namespace sprout {
+	namespace compost {
+		namespace formats {
+			//
+			// right_channel_forwarder
+			//
+			class right_channel_forwarder {};
+
+			//
+			// right_channel
+			//
+			namespace {
+				SPROUT_STATIC_CONSTEXPR sprout::compost::formats::right_channel_forwarder right_channel{};
+			}	// anonymous-namespace
+
+			//
+			// operator|
+			//
+			template<typename Range, typename T>
+			inline SPROUT_CONSTEXPR auto
+			operator|(Range&& lhs, right_channel_forwarder const& rhs)
+			-> decltype(
+				sprout::forward<Range>(lhs)
+					| sprout::adaptors::steps(2, 1)
+				)
+			{
+				return sprout::forward<Range>(lhs)
+					| sprout::adaptors::steps(2, 1)
+					;
+			}
+		}	// namespace formats
+
+		using sprout::compost::formats::right_channel;
+	}	// namespace compost
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_COMPOST_FORMATS_RIGHT_CHANNEL_HPP

sprout/utility/lvalue_forward.hpp

@@ -5,7 +5,7 @@
 #include <sprout/config.hpp>
 #include <sprout/utility/forward.hpp>
 #include <sprout/utility/as_lvalue.hpp>
-#include <sprout/type_traits.hpp>
+#include <sprout/type_traits/lvalue_reference.hpp>
 
 namespace sprout {
 	//